Catalytic cracking



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Patented Apr. 27, 1943 CATALYTIC CRACKIN G Charles E. Hemminger, Westfield, N. J., assigner to Standard Oil Development Company, a corporation of Delaware Application April 1, 1939, Serial No. 265,388

1 Claim.

This invention relates to improvements in the continuous conversion of relatively heavy hydrocarbons into valuable hydrocarbon fractions such as those boiling within the gasoline range.

The object of this invention is to provide a continuous catalytic process using such suitable apparatus including a catalyst conveying means as will enable eflicient and economical treatment of hydrocarbons.

In carrying the invention into elect, a catalyst conveying means, such as a Redler conveyor of the loop type, is employed to move the catalyst through a cracking or reaction zone. The conveyor lifts the catalysts against the oil vapors which iiow generally downwardly but with a stepwise to and fro transverse motion across the vertical column of rising catalyst, thus affording a substantially right angular ow of oil vapors with respect to the moving catalyst. Furthermore, the oil vapors enter the cracking zone at a point where the catalyst is least effective, i. e. contains greatest amount of poisons or contaminants and cracked vapors leave the reaction zone at a point about where fresh catalyst enters the reaction chamber. a solid siliceous material, a zeolite, coke, bauxite, clay or the like, is as indicated, during contact with heated hydrocarbon oil uid, poisoned or contaminated with a carbon containing material and consequently requires regular revivication after it has accumulated about 2% by weight or more of the poisons.

The poisoned catalyst leaving the cracking zone is discharged into an inclined chute or casing where it may be purged to drive off volatile hydrocarbons and then passes downwardly by gravity through a regeneration chamber comprising a plurality of vertical ducts disposed between baflied flues. A hot combustion supporting gas iiows generally upwardly but also laterally to and fro through the down flowing catalyst in a substantially right angular iiow with respect to the catalyst. The walls forming the catalyst ducts are perforated thus permitting the combustion supporting gas to flow into and out of the catalyst ducts. The result of the treatment of the poisoned catalyst with the combustion supporting gas is to burn 01T and/or oxidizc the catalyst poisons or contaminants causing impairment of its eiilciency. Fresh catalyst is co1- lected at the bottom of the regeneration zone and after purging with superheated steam or the like, is discharged into the tail portion of the conveyor and hoisted into the cracking zone as The catalyst which may befresh catalyst, thus completing a cycle of operations.

In the accompanying drawings, which illustrate one embodiment of my invention, selected for purposes of illustration,

Figure 1 is an elevational view partly in section, of an oil `cracking apparatus, suitable for carrying out this invention but not including the conventional preheating, fractionating and rening apparatus.

Figure 2 is a perspective View of a fragment of the cracking zone in the region of the oil inlet.

Figure 3 is a perspective view of the regeneration chamber interior showing the arrangement of catalyst ducts, flues, baiiles and cooling tubes.

Figure 4 is a fragmentary perspective view of the tail portion of the conveyor.

Referring to'Figs. 1 to 4 and speaking generi a cracking zone I a catalyst purging chamber 2, a catalyst regeneration chamber 3, and a second purging and conditioning chamber 4. The cracking zone l consists of two elongated fiues 5 carrying a plurality of bailies 6, constructed and arranged on opposite sides of conveyor 1. Referring at this point to Fig. 2 which shows an arrangement of conveyor and flues coming within the purview of this invention. the iiues 5 have the same depth as the casing of conveyor 1, as shown. The walls 8 of the conveyor 1 carry perforations 8a, thus permitting interiiow of oil vapors between flues 5 and conveyor 'l carrying catalyst C. In other words, flues 5 and the conveyor 'l have common walls 8 carrying perforations 8a lwhich perforations may be about 1%" in diameter and may be spaced apart from center to center an inch or so.

The conveyor, as a whole comprises a tail portion T, a main portion M, a head portion H and a loop L (see Fig. l). As may be seen from Figs.

2 and 4, the conveyor consists essentially of a` casing or well portion having four walls and may- '1 beneath hopper l5 for reloading with fresh catalyst,

Freshly prepared catalyst may be added to the system through manhole I6 of reservoir I4, or undesired catalyst may be there withdrawn.

Purgir'ig chamber 2 is formed by elevatable gates I8 and I9 and the portion of casing I1 therebetween. Purging gas inlet 20 is in communication with valved conduit 2l leading into cracking zone l, as well as conduit 22 leading into purging chamber 2. It is seen from Fig. 1 that catalyst C may be admitted for purging by gravity flow into chamber 2 by elevating gate I8. After the purging operation, gate I8 is lowered until it divides or separates the catalyst in I4 from that in chamber 2, and then the gate I9 is elevated permitting fiow of catalyst into regeneration chamber 3. When all of the catalyst has been discharged from chamber 2, gate I9 is again lowered and another charge of catalyst is admitted to the chamber 2 from reservoir I4 for purging. Reservoir I4 should be sufficiently large to permit continuous discharge of catalyst from conveyor 1 since, as explained, the operation of chamber 2 in purging is on intermittently moving catalyst.

The catalyst discharged from the chamber 2 falls by gravity through regeneration chamber 3 in ducts 22, the flow being directed into said ducts by virtue of crown pieces or caps 23. Each duct 22 is separated from the next duct by flues 24 carrying baiiies 25 (see Fig. 3). walls forming the catalyst ducts 22 carry perforations 36 throughout their length and breadth. These perforations may be about x36" of an inch in diameter and spaced apart an inch or so, from center to center. Flues 24 carry banks of tubes 26 through which water or some other cooling fluid may be circulated.

Referring now to Fig. 1, the regeneration chamber 3 is provided with a regeneration gas inlet 21, with recycle regeneration gas line 29 carrying pump 30 and with discharge conduit 28 through which gaseous products or vapors not to be recycled are withdrawn from the system.

As indicated by the directional arrows in Figs. 1 and 3, the construction and arrangement of ues and bafiies causes a generally upwardly, but also to and fro transverse flow of regeneration gas through the downcoming catalyst.

A receivingvessel 4 forms a temporary repository for catalyst regenerated in chamber 3. The

receiving vessel is provided with purging gas inlet 40. The purged catalyst is returned to the tail section T of conveyor 1 through hopper I5.

In order to give a specific example illustrating the present invention in actual operation, the

following description is given with the explanation that the invention is not limited by the precise details of said specific example.

Heated hydrocarbon vapors from any conveni tional source are introduced in chamber I through The vertical conveyor casing into one side of the rising solid column of catalyst C and to flow out through the opposite perforated wall 8 into the opposite flue, thence reverse its direction and flow through the column of catalyst in the opposite direction, but at a lower level, into the opposite ue. This type of ilow continues through the Whole length of the column of catalyst until finally the cracked products are withdrawn through conduit 5I. The

temperature of the catalyst should be in the neighborhood of 800830 F. and the pressure in the cracking zone should be about 5 lbs. per square inch on the gauge, but,'of course. good results can be obtained using lower pressures or considerably higher pressure. It is advisable, though not necessary toA introduce direct steam into the cracking zone as through pipes 2li and 2l. This steam actually assists in the cracking reaction and further tends to counteract or prevent the tendency of oil vapors to ascend toward chamber I4. Furthermore, housing 55 of loop portion L of conveyor 1 is preferably filled with steam admitted through inlet 52 and withdrawn through 53. This steam also forms a seal preventing the escape upwardly of oil vapors in the upper portions of flues 5.

Since the oil cracking reaction is cndothermic. it is desirable to dispose banks of tubes (not shown) in rlues 5 containing or flowing therethrough superheated steam and to cause the oil vapors to flow through said banks of tubes to compensate by heat transfer from the superheated steam for the heat lost during the cracking operation. The cracked vapors are withdrawn for fractionation through valved conduit 5 I- The column of catalyst proceeding upwardly is progressively contaminated by deposits resulting from the cracking operation until finally it becomes necessary to regenerate it. The length of the catalyst column should be such that too great an amount of deposit was not present on the catalyst before it was removed from the cracking chamber. That is to say, efficient operation may be achieved where the cracking zone is say 30 to 50 feet long. Furthermore, a catalyst column cross-sectional area of 2 feet by 4 feet gives good results.

The poisoned catalyst which has been lifted through the cracking zone is discharged into reservoir I4 and eventually flows into purging chamber 2. The operation in chamber 2 is intermittent and since catalyst is continuously discharged into I4, it is apparent that I4 must be of suicient relative size with respect to chamber 2 to accommodate this situation.

Assuming chamber 2 is empty, the same is filled by lifting gate I8 to the height shown in Fig. 1, while gate I9 is lowered.v When the chamber 2 is lled, gate I8 may be lowered. A purging gas, such as superheated steam at a temperature of say between '100 F. and 830 F. is forced into chamber 2 through conduits 26 and 22 and withdrawn through exhaust line 60. Instead of using steam, flue gas, nitrogen, carbon dioxide or mixtures thereof may be used for purging.

Following purging, the catalyst is discharged into regeneration chamber 3 by raising gate I9. The catalyst falls through ducts 22 to a receiver 4. Meanwhile, air or some oxygen-containing gas is admitted through line 21 :Into the bottom of the regeneration chamber. This air or other regeneration gas may have an inlet temperature of about 700 F. and is caused to l flow laterally through descending catalyst and also stepwise upwardly by the baiiies 25 toward outlet pipe 28. The regeneration gas flows through the perforations 36 in the walls of the catalyst ducts from the fiues into the ducts and out again in a cross-wise reversing ow. Arriving at about the region where the inlet pipe 29 is attached to the regeneration chamber, the air or other gas is admixed with recycle gas consisting largely of carbon dioxide and steam. The

admixture causes a reduction in the oxygen con'- centration of the regeneration gas to about more or less.

At about midway between the point where recycle gas enters chamber 3 and the products of combustion are withdrawn, the oxygen concentration should be about 5%, whereas near the top of the regeneration column, the oxygen concentration is about 2%. The advantage of this oxygen concentration gradient is that the most highly contaminated catalyst encounters a low oxygen concentration, while toward the end of the regeneration a high oxygen concentration, say or more, is encountered by the catalyst in removing the last traces of tar material or coke. The oxygen concentration of the regeneration may vary from at the inlet to 10% at the outlet. It may be advisable to, in certain in-l stallations, provide two or more recycle gas inlets obtain the desired oxygen concentration gradient. It may also be advisable to provide ducts 22 with a number of steeply inclined bailles to cause the downcoming catalyst to describe a somewhat tortuous path.

The oxygen-containing gas or the pure air, as the case may be, causes, upon contact with the catalyst, combustion or oxidation or distillation of the poisons or contaminants of catalyst C during its passage through chamber 3. The temperature of the combustion reaction can be controlled by circulating a cooling fluid such as cold water through coils 26 (see Fig. 3). Temperature indicating devices, such as thermocouples (not shown) should be disposed in the flues at several points through the length of g the regeneration chamber and, based on such readings or indications, the temperature of the catalyst at any time during regeneration should be maintained below 1150 F. in the case of most catalysts.

The gas pressure prevailing in the regenerator should be between 5 pounds per square inch and lbs. per square inch with about 40 lbs. per square inch preferred.

Finally, the regenerated catalyst, which has fallen to chamber 4 is again purged and conditioned by superheated steam or the like introduced through valved conduit 40 and thereafter immediately discharged into hopper I5 and thence directly into the tail of the Redler conveyor for reintroduction into the cracking chamber I.

Numerous modifications may be made in the invention as above disclosed without departing from the spirit thereof. For example, the catalyst conveyor need not be a Redler type, but might be a belt or bucket conveyor. The regeneration chamber 3 may be square, rectangular or circular in cross section. Furthermore, a powdered,'granular or lump catalyst may be employed. In the case where a powdered catalyst is employed, the perforations in the casing of the conveyor and the ilue walls may require reduction in diameter from about 11g to 1/8 inch. Various other modifications falling within the scope of the invention are permissible without departing from the spirit of the invention.

I claim:

A process for catalytic conversion of hydrocarbons which comprises continuously moving a column of catalyst particles upwardly through a conversion zone, introducing heated hydrocarbon vapors into the top portion of said column. passing the heated hydrocarbon vapors transversely through the upwardly moving column of catalyst particles and back and forth through said column at lower levels and removing cracked vapors from the bottom of said catalyst zone.

CHARLES E. HEMMINGER. 

